Means for exciting the commutating-poles of a dynamo-electric machine.



J.-L. WOODBRIDGB. MEANS FOR EXCITING THE GOMMUTATING POLES OF A DYNAMOELECTRIC MACHINE.

APPLICATION FILED JUNE 8, 1912.

Patented M31. 2, 1915.

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WITNESSES:

J. L. WOODBRIDGE. MEANS FOR EXCITING THE GOMMUTATING POLES OF A DYNAMOELECTRIC MACHINE. -APPLIOATION FILED JUNE 8, 1912.

1,130,686. Patented Mar. 2, 1915.

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NOIRIS'PETERS C0 PHOTO-LITHO WASHINGTON. D C.

JOSEPH LESTER WOODBRIDGE, OF PHILADELPHIA, PENNSYLVANIA.

MEANS FOR EXCITING THE COMMUTATING-POLES OF A DYNAMO-ELECTRIC MACHINE.

Specification of Letters Patent.

Application filed June 8, 1912.

T all whom it may concern:

Be it known that l, Josnrrr LESTER 00D- BRIDGE, a citizen of the UnitedStates, and a resident of Philadelphia, State of Pennsylvania, haveinvented certain new and useful Improvements in Means for Exciting theCommuteting-Poles of a Dynamo-Elec trio Machine, of which the followingis a specification.

My invention relates to dynamo electric machines in which bothalternating currents and direct currents are delivered to or receivedfrom the same armature, and in which commutating poles are employed toproduce sparkless commutation. Synchro nous converters or double currentgenerators adapted to deliver both alternating and direct currents fromthe same armature may be mentioned as examples. My in vention is equallyapplicable whether the armature of the machine has a single wind ingconnected to a commutator and to collector rings, or has two windings,one of which is connected to the commutator and the other to thecollector rings. My invention is particularly applicable to those casesin which the alternating currents and the direct currents, which arecarried by the armature windings, do not bear a fixed relation to eachother.

In a synchronous converter, as ordinarily operated, the direct currentoutput is directly proportional to the energy component of thealternating current input. The armature reactions of these two currentspractically neutralize each other. In designing a commutating pole forsuch a machine, it is, therefore, only necessary to provide ex citationsufiicient to develop the commutating flux necessary to reverse thecurrent in the coil which is passing under the brush, and no additionalexcitation to compensate for armature reaction is required. Thecommutating flux required is practically proportional to the directcurrent output, and a series winding carrying this output, or a currentproportional thereto, will give sat isfactory results. In the doublecurrent generator, and in special types of synchrono us vconverters,these conditions do not exist,

and the armature reaction of the alternating current and the directcurrent do not cancel each other, and these currents are notproportional to each other. In such cases it is necessary to provideadditional excitation on the commutating poles to bal Patented Mar. 2,1915.

Serial No. 702,428.

ance the armature reaction, and inasmuch as this armature reaction isnot proportional to the direct current output a series winding will notgive the desired results. As examples of machines in which theseconditions of unbalanced armature reaction occur may be mentioned thesplit pole converter and the synchronous converter which in addition toits function as a converting device be tween alternating currents anddirect currents is operating as a motor to deliver mechanical energyfrom its shaft, as, for example, to a booster mechanically driven by theshaft of the converter. In order to provide suitable excitation for thecommutating poles of such machines I propose to provide means forexciting these poles with currents proportional to the algebraic sum ofthe direct current input or output from the DC brushes and thatcomponent of the alternating current input or output whose armaturereaction is in line with the commutating poles.

My invention will be more clearly understood by reference to thefollowing description taken in connection with the accompanyingdrawings, in which,

Figure l is a diagrammatic view illustrating features of my invention inconnection with a split pole converter, while Fig. 2 illustratesfeatures of the invention modified as to some of the details and appliedto a synchronous converter driving an alter nating current booster.

Referring to Fig. 1, A is a source of three phase alternating currentsupplying the circuit 1, 2, 3 to which are connected translating devicesL 4, 5 is a direct current circuit to which are connected the storagebuttery B, and translating devices such as the motor M and lamps L. R isa rotary converter of the split pole type connected be tween thealternating current circuit and the direct current circuit. 25 and 26are the direct current brushes of this machine, and 19, 20 and 21indicate the points in the armature winding from which taps are takenfor connection to the alternating current circuit.

It will be understood that these latter connections are made in theusual manner by means of slip rings which have been omitted from thedrawing in order to avoid confusion. The main poles P of the converter Rand the regulating poles P as here shown, are excited by independentcircuits connected across the circuit 4, 5 with rheostatic control. Itwill be understood, however, that any of the well known manual orautomatic methods of exciting these poles may be adopted. Thecommutating poles P of this machine are excited by windings 17 and 18which are connected in series across the main brushes 15, 16 of theexciter E. This exciter is, in general, similar to that de scribed in myPatent No. 870,150 and is so designed as to furnish current to thewindings 17 and 18 which is proportional to the difference between thedirect current output of the converter R and the alternating currentinput. This result is accomplished by reason of the special design oftheexciter E as follows: The armature winding of this machine is connectedto a commutator X and also has six-phase taps at the points 7, 8, 9, 10,11' and 12. These la tter points are connected diametrically to thesecondary windings of three current transformers T T and T whose primarywindings are connectedinseries with the alternating current leads of theconverter It. By this means alternating currents proportional to thealternating current input to the converter R are passed through thearmature winding of the exciter and if the armature werestationary thesecurrents would produce a rotating field in said armature. This armature,however, is mounted on shaft H of the converter R, and thereby rotatedin the opposite direction to that of the induced field rotation, thusproducing a field which is stationary in space in the direction of thearrows K The poles of the exciter E are provided with a winding 6connected in series with one of the direct current leads ofthe converterR, this winding being so connectedas to produce a field in the oppositedirection to the arrows K The direct current output of the exciter takenfrom the brushes 15, 16 will also produce an armature reaction in thedirection of the arrows'l 1 and opposed to the excitation produced bythe windings 6. Under normal conditions of operation these three sourcesof field excitation, namely, the AC input from the current transformersT T9 and T the DC excitation in thewindings 6 and the DC armaturereaction from the brushes 15 and 16 will nearly balance each, other,leaving a small residuum which will produce a field flux in the line ofthe arrows K thereby producing a small electro-motiveforce acrossthebrushes 13 and 14;. These brushes are short-circuited so thatthiselectro-motive-force will produce an appreciable flow of current which,by reason of the armature reaction, will produce a field at right anglesto the arrows K and an. electromotive-force between the-brushes 15 and16 sufficient. to produce the required flow of current in the windings17 and'18. As explained above, this flow of current will always be suchas to produce approximate able for giving the excitation to itscommutating poles.

One of the peculiar features of the split pole converter It is the factthat when the excitation of the regulating poles P is altered in orderto change the ratio between AC and DC electro-motive-force, the meanline of the total field flux is shifted in one direction or the other,followed by a shift in the phase position of the armature. This shiftsthe axis of the AC armature reaction, so that if before the shift theentire alternating current were effective as a factor in determining theexcitation for the commutating poles, after said shift only onecomponent of this alternating current will be thus efiective. Bymounting the armature of the exciter E on the shaft of the converter, orby driving it in any other way mechanically from the shaft, this shiftof phase position in the converter will be followed by a correspondingshift in phase position in the exciter, so that the same component ofthe alternating current, which is effective in the converter B, willalso be effective in the exciter'E.

In Fig. 2 instead of a split pole converter, there is shown a standardconverter R with an alternating current booster G mounted on its shaft.This booster is provided with 3 phase armature windings 22, 23 and 2-1connected in series between the AC circuit'l, 2, 8and the armature ofthe converter R It will be understood that the main poles P of theconverter R as well as the poles P* of the booster G, may be excited byanw ofthe well known means either manually controlled or automatic, butin order to simplify the drawing no windings have been shown on thesepoles. The commutating poles P of the converter R are each provided withtwo windings. One of these windings 27 is connected in series with oneof the direct current leads of the converter. The other winding '28 issupplied with current from the exciter E This latter is different indesign from the exciter E shown in Fig. 1, but is similar to the machinedescribed in my Patent No. 870,149. It consists of'a magnetic circuit 0,all parts of which are relatively fixed, upon which is wound a winding29 similar to an armature winding and threaded through openings 30 inthe magnetic circuit. No external stationary field circuit is provided.The machine E is driven by the synchronous motor D connected to thecircuit 1, 2, 3 whose field is shown at F. The commutator Z is connectedto the winding 29 in the usual manner, and on this commutator bear 4brushes 31, 32, 33 and 3%. Brushes 32 and 34: are short circuited, Whilebrushes 31 and 33 are connected to the Winding 28 on the commutatingpoles of the converter R The winding 29 is also connected at 3 points35, 36 and 37 by means of suitable slip rings, not shown in the drawing,to the secondaries of 3 current transformers T, T and T, whose primariesare connected into the alternating current leads of the converter R Thealternating current thus introduced into the winding 29 will produce afield which is held stationary in space by the rotation of the motor D.This field will be in the direction to produce an electro-motive-forceacross the brushes 32 and 34. The flow of current through the shortcircuit between these brushes will produce a field at right angles tothe first, and an electromotiveforce across the brushes 31 and 32, whichwill send current of the desired value through the windings 28. Thislatter current will be substantially proportional to the alternatingcurrent from the transformers T", T and T and, in fact, will nearlyequalize the effects of these latter currents in the exciter E leaving asmall residuum sufiicient to produce the necessary flow of currentacross the short circuited brushes. It will be seen, therefore, that thetotal excitation of the commutating poles P is proportional to thedifference between the direct current output and the alternating currentinput of the converter R If the apparatus is properly designed, theexcitation of these poles will, therefore, be suitable for producingsparkless commutation regardless of the proportion of the AC input andthe DC output. In the case of the standard converter shown in Fig. 2there is no shifting of the mean line of the field flux, and it is,therefore, not necessary to provide for this phenomenon in driving theexciter E. A synchronous motor drive will, therefore, be suitable inthis case. I

Having described my invention what I claim and desire to secure byLetters Patent 1s,

1. In combination, an armature having both alternating current anddirect current external connections, a commutating pole for saidarmature, means responsive to both the alternating and the directcurrent flow through said connections for exciting the commutating pole,main poles for said armature and means for developing in said main polesa field flux independent of the flux in said commutating pole.

2. In combination, converting apparatus including a field structure andits correlated armature whereof the field structure is provided withcommutating poles and their windings, and the armature is provided withalternating current and direct current terminals, means for furnishingto said coinmutating poles excitation proportional to the combined flowof direct current and alternating current to or from said terminalsrespectively, said means including a synchronously driven exciterprovided with an armature winding and its commutator, means forsupplying to said armature winding alternating currents proportional tothe alternating current fiow at the alternating current terminals of theconverting apparatus, and two sets of brushes for the commutator whereofone set is connected to windings on the commutating poles of theconverting apparatus and the other set is interconnected by anindependent conducting circuit.

3. In combination, a synchronous converter of the split-pole type havingmain poles, regulating poles and commutating poles with theirappropriate windings, alternating current and direct current leads forsaid converter, and exciter for the commutating poles including anarmature winding and its commutator, current transformers having theirprimary windings connected into the alternating current leads of theconverter and their secondary windings connected to the armature windingof the exciter, two sets of brushes for the exciter commutator whereofone set is short-circuited and the other set is connected to thecommutating pole windings of the converter, means for driving theexciter in synchronism with the converter, and means for furnishing tothe commutating poles of the converter a component of excitationproportional to the current flow in the direct current leads.

In testimony whereof I have hereunto signed my name.

JOSEPH LESTER WOODBRIDGE.

Vitnesses:

J. H. TRACY, R. A. VVHnTs'roNE, Jr.

Copies 0! this patent may be obtained for five cents each, by addressingthe Commissioner of Patents,

Washington, D. 0.

